It has been known to provide plug connectors in explosion-proof operating means, which plug connectors can be used in potentially explosive areas. In conjunction with this, publication EP 1 638 173 A2 suggests plug connectors comprising several contact pins. One of the contact pins is disposed to contact a monitoring conductor. This contact pin is slightly shorter than the other contact pins so that it is the last to act as a contact when the plug-in connection is established and the first to disconnected when the plug-in connection is severed. A voltage is applied to the monitoring conductor, said voltage being below the minimum ignition voltage. Consequently, when the contact point is opened and closed, it is not possible for ignition sparks to form. By means of the monitoring conductor, the power supply to and from the other, longer, contact pins is switched on and switched off. As a result of this it can be ensured that the other, longer, contact pins are always in contact with the respectively allocated sockets in currentless and voltageless state. The combination of a monitoring conductor complying with the type of explosion protection Ex i with other contacts that are closed or opened only in currentless state requires additional switches in the connected components.
Furthermore, publication DE 20 2005 010 927 U1 discloses an explosion-proof plug connector of the ignition protection type pressure-proof encapsulation (Ex d). It is designed in such a manner that the pressure-proof encapsulation is maintained until all contacts are disconnected.
Explosion protection by pressure-proof encapsulation of all contacts results in considerable design and structural expense.